Nutrition and Reproduction in Modern Dairy Cows

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The Mid-South Ruminant Nutrition Conference does not support one product over another

and any mention herein is meant as an example, not an endorsement.

2010 Mid-South Ruminant Nutrition Conference 51 Arlington, Texas

Nutrition and Reproduction in Modern Dairy CowsRalph G. S. Bruno, DVM, MPVM

Texas AgriLife Extension Service

Texas A&M System and West Texas A&M University

INTRODUCTION

Genetic improvement programs have done a

great job selecting animals with superior genetics for milk production. Selection with emphasis on milk

production is generally recognized as the single most

important objective of breeding programs in dairy

cattle worldwide. As a result of this improvement, thedairy cow has changed significantly over the past 7

decades with a remarkable increase in milk

production/lactation (Butler, 2000). Comparing the

shape of lactation curves from a dairy cow from the

1940s with today’s dairy cow, it is evident that themilk yield/lactation is almost 5 fold higher than in the

1940s. However, comparing reproductive

performance, the modern dairy cow has decreasedfertility (Butler, 2000) which has become the number

one reason for involuntary culling (NAMHS, 2007).

Several reasons for reproductive failure existincluding: nutrition, management, disease, and

intrinsic physiological factors. In order to maintain

high levels of milk production, modern dairy cows

are under a constant challenge to meet nutritionaldemands and are more likely to experience adverse

postpartum diseases and reproductive failure.

Numerous recent studies have reported this negativecorrelation between high levels of production and

reproductive performance. Lucy (2001) attributes this

decrease in fertility not only to increased milk

production, but also to adverse events surroundingthe periparturient period. These events do not impair

reproduction directly, but affect animal health with

undesirable effects carried over throughout the entire

lactation.

Nutritional management of a dairy cow, mainly

during periods of high levels of stress, is an important

tool to improve animal health and reproduction.

During late pregnancy and early postpartum, thenutritional requirements of a dairy cow significantly

increase to support fetal growth, mammogenesis, and

lactogenesis; at the same time that dry matter intake(DMI) decreases. After parturition nutritional

requirements remain elevated to support incremental

increases in milk yields until lactation peak. During

this period, diets must be designed to minimize the

losses in body condition score (BCS) observedduring the negative energy balance (NEB) period,

which is the period when nutrient requirements for

maintenance and lactation exceed the ability of the

cow to consume sufficient energy from feed. It iswell documented in the literature the negative effect

NEB has on animal health and reproduction. When

cows experience a period of NEB, blood levels of

nonesterified fatty acid (NEFA) increase as aconsequence of body energy reserve mobilization

(adipose tissue), at the same time insulin-like growth

factor-I (IGF-I), glucose, and insulin are low. Thesemetabolic changes might compromise animal health,

ovarian function, and fertility.

In each period of lactation, nutritional strategiesmust be customized to improve animal health and

reproduction without interfering with lactation

performance. These strategies, when used wisely, can

positively impact animal performance and improve

the efficiency of a dairy operation. However, goodmanagement practices must be in place in order to

observe these diet effects.

POSTPARTUM DISEASES AND THE

NUTRITION OF TRANSITION COWS

Postpartum Uterine Diseases

The postpartum period is one of the most critical

stages of lactation for a high producing dairy cow. It

is characterized by drastic metabolic changes,immunosuppression, NEB, and elevated levels of

stress; which can lead to increased incidence of

diseases and decreased animal efficiency. Most of theevents observed in this period (ketosis, milk fever,

retained placenta, metritis, etc.) have some effect on

animal performance, mainly on subsequent fertility(Ferguson, 2000). Cows diagnosed with postpartum

uterine diseases (metritis, clinical or subclinicalendometritis) had decreased odds to conceive at the

first AI and experienced extended periods until

conception (Ferguson, 2000; Bruno et al., 2007).These postpartum reproductive diseases are linked to

the nutritional status of animals. Recent studies have

linked postpartum uterine diseases with reduced






feed intake (Hammon et al., 2006; Huzzey et al.,

2007). In both studies researchers observed that cows

developing metritis (severe or mild) or endometritis

had decreased DMI beginning 2 wk prior to calving.

A similar study, evaluating behavior of dairy cowsduring the periparturient period, indicated that cows

experiencing acute metritis spent less time eating

than cows without acute metritis (Urton et al., 2005). Not only are clinical uterine diseases negatively

correlated with reproduction, subclinical endometritis

has also been linked with impaired fertility (Bruno et

al., 2007). Subclinical endometritis is characterized by a large intrauterine influx of neutrophils without

clinical signs. Cows identified with subclinical

endometritis at 35 d postpartum had lower conception

rates at first AI and experienced an extra 27 d toconception compared to cows classified as having

normal uterine health (Bruno et al., 2007).

The increased incidences of periparturient

diseases also are associated with physiological postpartum immunosuppression. Causes of this

impairment of the immune status around calving arenot completely elucidated yet, but it is the

consequence of multiple factors observed during this

period such as fetal corticoid release, NEB, increased

blood levels of NEFA, imbalance of Ca and glucose

metabolism, and decreased DMI. Thisimmunosuppression is characterized by reduced

neutrophil function and decreased production of

lymphocytes beginning up to 2 wk prior to calvingand extending until 3 to 4 wk postpartum (Kehrli et

al., 1989). Hammon et al. (2006) evaluated neutrophil

function during the postpartum period of 83 periparturient cows, studying the killing ability of neutrophils correlated to blood levels of NEFA

during the transition period. In this study researchers

observed that cows diagnosed with puerperal metritis

(within 14 d postpartum) or subclinical endometritis(within 28 d postpartum) had significantly lower

neutrophil activity than cows classified as having

normal uterine health. They also observed that thecows diagnosed with puerperal metritis or subclinical

endometritis had significantly lower DMI and

increased levels of NEFA and Β-hydroxybutyrate

(BHBA) starting prior to calving. These changes in

the metabolic profile of lactating dairy cows arecommonly observed during NEB period, which has

been associated with postpartum immunosuppression.

These data clearly identify suppressed nutrientintake prior to calving as a major risk factor for

postpartum uterine diseases and consequentlyimpairment of subsequent fertility. Nutritional

management in the periparturient period should be

designed to prevent or minimize DMI suppression in

order to improve uterine health.

Metabolic Diseases

Negative energy balance and mineral imbalance

early postpartum has been attributed to several

postpartum disorders compromising dairy cowfertility. Deficiency of Ca during this period is a

major problem in high producing dairy cows. There

is no other period in a dairy cow’s lactation in which

Ca requirements are higher than the period aroundcalving. Calcium is required for numerous vital

functions, for example acting as a second messenger

or co-factor for intracellular metabolic pathways,

milk synthesis, and muscle contractions in organssuch as the diaphram, rumen, lungs, mammary gland,

liver, and uterus. As parturition approaches, a high

demand for Ca is required for colostrum productionas well as for contraction of all the muscles involved

in the parturition process. Reviewing briefly peripartum Ca requirements, shortly before calving

the mammary gland extracts a large amount of Cafrom the blood and incorporates it into colostrum.

The normal blood level of Ca is approximately 8.5 to

10 mg/dL, which means there is approximately 3.5 g

of Ca, (ionized Ca) in the entire plasma pool of an

adult Holstein cow weighing 600 Kg. The Caconcentration in the colostrum ranges from 2 to 3 g/L

of colostrum. A cow producing 15 L of colostrum has

approximately 30 g of Ca, which was transferredfrom the blood to the mammary gland; meaning 10

times more Ca was required than the free form of Ca

present in the cow’s plasma. With this deficit of Ca,subclinical or clinical signs of hypocalcemia can beobserved.

Several studies have reported the deleterious

effect of hypocalcemia on subsequent fertility.Whiteford and Sheldon (2005) reported that cows

experiencing hypocalcemia had increased incidence

and severity of uterine diseases and delayed return of ovarian cyclic activity. Moreover, cows experiencing

hypocalcemia were 3 times more likely to experience

retained placenta than cows not experiencing this

disease (Curtis et al., 1983). Hypocalcemia can also

affect dairy cow fertility indirectly. Hypocalcemiccows at parturition had 4.8 times greater risk of

developing left displacement of abomasum (LDA)

than normocalcemic cows (Massey et al., 1993) and

cows experiencing LDA had delayed postpartum firstservice (Raizman and Santos, 2002).

Nutritional efforts to prevent clinical or

subclinical hypocalcemia may improve reproductive

efficiency of high producing dairy cows. Several






nutritional strategies have been proposed to minimize

the Ca imbalance in the periparturient period. One of

these strategies, widely used in large dairy

operations, is dietary cation-anion difference

(DCAD) diets fed throughout the last 21 d before theexpected calving date. The DCAD diet consists of

addition of anionic salt to the prepartum diets, which

creates a slightly metabolic acidosis status; thereforeincreasing Ca mobilization. Although this strategy is

very effective in preventing and minimizing the

incidence of hypocalcemia, adding anionic salts to

prepartum diets can inhibit DMI due to palatabilityissues leading to different metabolic distresses, which

also have negative effects on animal health and

reproduction. Monitoring DMI and urine pH often

are necessary tools for the success of DCAD diet.

Energy metabolism during the transition period

plays an important role on animal health andreproduction. Energy requirements at the end of the

gestational period and initiation of lactation alwaysexceed the amount of energy the cow obtains from

her diet. It is estimated that in the last week of fetaldevelopment the fetus uses approximately 46 % of

maternal glucose taken up by the uterus (Bell, 1995)

and the onset of milk production makes this energy

shortage even more remarkable. The mammary gland

drains a large amount of glucose to synthesize milk lactose through its predominant glucose transporter

GLUT-1; which does not require insulin for glucose

uptake. Rigout et al. (2002), studying glucosemetabolism in dairy cows, concluded that the

mammary gland consumes 60 to 70 % of the whole

body glucose, mainly for lactose synthesis. In thiscase, a cow producing 30 Kg of milk per day uses atleast 1.5 Kg of blood glucose to synthesize milk

lactose. The high demand of energy during this

period of glucose shortage triggers a compensatory

process of nutrient partitioning and adipose tissuemobilization. However, there is a limit to the amount

of fatty acids that can be metabolized by the liver in

order to be converted to energy. When this limit isreached, fats are no longer oxidized and start to

accumulate as triglyceride in hepatocytes leading to

hepatic lipidosis (fatty liver syndrome). Cows

experiencing fatty liver syndrome experience

extended periods to first ovulation (Reist et al., 2000)and reduced reproductive performance (Jorritsma etal., 2000). Ketone bodies are formed as a result of β-

oxidation of fat, which is used as energy. The excess

ketone bodies are eliminated in the urine and milk

and are observed during clinical and subclinical casesof ketosis. A meta-analysis indicates that clinical

ketosis is associated with an increase of 2 to 3 d tofirst service and with 4 to 10 % fewer pregnancies

per AI at first service (Fourichon et al., 2000).

Duffield (2000) reported that fat cows (BCS ≥ 4.0)

had elevated blood levels of BHBA postcalving and

were at higher risk of developing subclinical ketosiscompared to cows classified as moderate or thin BCS

prior to calving. In addition, subclinical ketosis has

also been liked with increased incidence of ovariancysts (Duffield, 2000).

Because increased energy demand is observedeven before calving, strategies to prevent metabolic

disease have focused on the nutritional management

of the dry and transition cow. The goals of these diets

are basically to provide all required nutrients and toadapt the rumen for diet changes as cows advance to

different stages of lactation. Diets must beformulated in order to accomplish this goal and also

minimize DMI change to prevent metabolic and

uterine diseases. Managing BCS towards the end of

the lactation is another important management practice in order to minimize postpartum diseases.

NUTRITION INTERACTION WITH

POSTPARTUM OVULATION

RESUMPTION

In all mammalian species, resumption of

cyclicity requires that all organs and tissues

associated with reproduction recover from the

previous pregnancy and parturition:

• Ovaries must re-establish full follicular development with ovulation;

• Hypothalamus/pituitary glands must secrete

gonadotropin hormones in an appropriatemanner to stimulate follicle growth; and

• Liver must be adapted to support heavymetabolic loads (Butler, 2005).

However, in dairy cows the re-establishment of all

these functions is negatively correlated to NEB. After

parturition, nutritional requirements increasedramatically with each increment of milk production

and the resulting NEB can extend up to 8 to 10 wk after calving, delaying resumption of ovulation to 10

to 14 d after the nadir of NEB (Butler, 2003).

During the NEB period, homeorrectic controls

assure nutrient partitioning and adipose tissue

mobilization to support milk production. During this period it is common to observe losses in body weight

and BCS. Santos et al. (2009), evaluating changes in

BCS, reported that severe weight and BCS losses dueto inadequate nutrition or diseases are associated with

anovulation or anestrus status in dairy cows. In fact,

cows with poor BCS are more likely to be anovular,which compromises dairy cow fertility (Bruno et al.,

2005). Reasons for anovulation during the NEB






period include attenuation of luteinizing hormone

(LH) pulse frequency and low levels of blood

glucose, insulin, and IGF-I that collectively limit

estrogen production by dominant follicles (Butler,

2005).

Fertility of dairy cattle is affected by NEB by

inhibition of ovulation in early lactation, reduction of estrous expression and impairment of conception and

embryo survival during the breeding period (Santos

et al., 2004). Several studies have demonstrated

improvement in estrous expression, conception rate,and embryo survival when resumption of ovulation is

observed prior to the initiation of synchronization

programs for first postpartum AI (Bruno et al., 2005;

Santos et al., 2004).

Resumption of ovarian activity in high producing

dairy cows is determined by energy status of theanimal. Nutritional management, to minimize the

inhibitory effects of NEB on resumption of ovulationand to prevent postpartum metabolic diseases, should

begin during the prepartum period. These strategiesshould include maintaining moderate BCS and

energy intake throughout the transition period.

NUTRITION INTERACTIONS WITH

THE BREEDING PERIOD

Most dairies start re-breeding their cows between50 and 70 d after calving. It is expected that by this

time the majority of cows are completely recovered

from their previous calving and are ready to conceive

again. However, reproductive and nutritionalmanagement during this period is important for asuccessful reproductive program.

The beginning of the breeding season coincideswith the period in which cows are reaching or are

about to reach the peak of milk production, which

generally occurs around 6 to 9 wk postpartum.

Targeting higher peak milk production, diets offeredat this stage are designed to maximize DMI.

However, increased DMI is associated with an

increased rate of metabolism of reproductive

hormones (Rabiee et al., 2001) impairing

reproductive performance. High producing dairycows have increased DMI due to lactation

requirements. Lopez et al. (2004) reported that cows

with milk production above herd average (39 Kg/d)had shorter duration and lower intensity of estrus

than cows with lower milk production. This negative

effect of DMI on estrous expression is explained bythe increased liver blood flow decreasing the

concentration of plasma hormones, including steroids

and consequently changing estrous behavior.

Identification of feedstuffs that potentially can block

hepatic steroid metabolism is currently under

investigation at the University of Wisconsin-Madison

and is not ready to use on dairy farms. Another potential strategy to overcome poor estrous

expression is through supplementation of steroid

hormones to improve reproduction, although none areapproved for use.

On the other hand, cows not consuming enough

until peak lactation lose BCS and have decreasedreproductive performance. Santos et al. (2009)

evaluating changes in BCS in early lactation

concluded that cows losing one or more units of BCS

from calving to the time of first AI were less likely toconceive and were at higher risk of losing their

pregnancy. Moreover, cows with BCS lower than 3.0

at the time of AI had the lowest risk for pregnancycompared to cows with better BCS (Santos et al.,

2009).

Nutritional strategies to improve reproductive performance during this period include increasing the

energy density of the diet, which can be done with fat

supplementation. Fats in the diet of a dairy cow can

positively influence reproduction by altering both

ovarian follicle and corpus luteum function viaimproved energy status and by increasing precursors

for the synthesis of reproductive hormones, such as

steroids and prostaglandins (Mattos et al., 2000).However, different degrees of saturation might

influence fertility outcomes. Juchem (2010)

evaluated the effect of feeding protected fat as Casalts and observed increased conception rates in cowsfed Ca salts of linoleic and monoenoic C18 trans

fatty acids (unsaturated fatty acids) compared with

cows fed Ca salts of palm oil (highly saturated fattyacid). This improvement in fertility was attributed to

higher fertilization rates (87.2 % versus 73.3 %), and

the greater proportion of embryos graded as 1 and 2(73.5 % versus 51.5 %), for saturated and unsaturated

fatty acid diets respectively (Cerri et al., 2009).

NUTRITION AND LATE LACTATION

INTERACTIONS

Towards the end of lactation it is expected thatall cows in the herd are pregnant; therefore the

nutritional goal during this period is to maintain

pregnancy and prepare cows for the next lactation.

After 90 d of gestation, few cows lose their

pregnancy (Santos et al., 2004) unless a major stressor such as a disease outbreak, heat stress,

mycotoxin from spoiled feed, etc. are present. During






this period diets must be formulated to support fetal

growth and milk production, dependent upon stage of

lactation, without allowing cows to gain excess BCS.

Cows overconditioned prior to calving are at a higher risk of developing metabolic diseases and are more

likely to be culled involuntarily at the beginning of

the next lactation. During this period providinganimal comfort, clean water, adequate nutrition, and

minimal stress are important features in minimizing

pregnancy loss; which is critical for cows in latelactation.

CONCLUSION

Genetic selection in dairy cows during the last

decades has focused mainly on milk production. As

cows became more specialized in producing milk, anincreased likelihood of health disorders and

reproductive failure has been observed. Studies have

shown that nutritional management during the

transition period can improve uterine health and

minimize metabolic distress in the postpartum period.

Managing negative energy balance by increasing

energy intake during the early postpartum and breeding period may improve resumption of cyclicity

and reproductive outcomes. Supplementation with

unsaturated fat can improve fertility, as long as it is protected from rumen biohydrogenation of fatty

acids. Nutritional management during the late

lactation period must meet nutritional requirements

for production and fetal development without

allowing cows to become obese, which negatively

impacts animal performance in the followinglactation.

Managing a high producing herd andmaintaining high reproductive performance is an

enormous challenge for the dairy producer. Nutritionists and veterinarians must work together to

ensure that producers are applying all the currently

known facts about nutrition, herd health, and

reproduction on a daily basis. Proper nutrition is part

of a successful reproduction program; but absence of

any one of the other key management componentslikewise can result in a poor herd reproduction

program.

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Nutrition and Reproduction in Modern Dairy Cows